Edo Tensei
The 'Summoning: Impure World Reincarnation'binds the soul of a deceased person to a living vessel, restoring them as they were when they were alive in order to do their summoner's bidding. It was originally created by Tobirama Senju, after which he declared it a kinjutsu. Orochimaru rediscovers the technique decades later, and Kabuto Yakushisubsequently perfects it. Usage Before this technique can be performed, the user must first acquire some of the DNA of the person they intend to reincarnate. Kabuto remarks that this basically amounts to grave-robbing, although blood stains or organs salvaged after the target's death also work.2 The soul of the intended reincarnated must also reside in the Pure Land; souls trapped in the stomach of the Shinigami, for example, cannot be reincarnated so long as they reside there.3 A living sacrifice is also required for the reincarnated soul to use as a vessel.2 To actually perform the Impure World Reincarnation, the DNA of the person to be reincarnated is smeared on a special scroll. Once the scroll is activated, the remains spread out in the form of a special seal with the living sacrifice in the centre. Then dust and ash encase the sacrifice's body, giving them the same appearance that the reincarnated had at the time of their death; the process is apparently painful for the sacrifice.2 The sacrifice's chakra signature is completely overridden with the chakra of the one being reincarnated. Although the sacrifice is still technically alive so long as the technique is active, their body will never again be theirs and the body will die when the reincarnated soul is released. Although Tobirama was the technique's creator, his usage had two flaws: the reincarnated souls were not as powerful as they were while alive and he could only control so many at a time.4Orochimaru is stated to have mitigated both flaws somewhat, but it is Kabuto who entirely eliminates them, perfecting the Impure World Reincarnation to such a degree that the reincarnations are practically as they were during life and he can control as many at a time as he wishes to, resources permitting.2 His improvements, combined with the fact that performing the Impure World Reincarnation requires no chakra from the user, causes Kabuto to declare it the most powerful jutsu in history.4 Reincarnations can be mobilized like standard infantry, where they must travel to their destination. Alternatively, coffins that contain them can be summoned to a location, assuming someone is there to perform the summoning; the anime does not consistently require this.5 Reincarnations can be recalled in a similar way, with a coffin emerging around them to take them back. Control Edit The only discretion a user needs to exercise for the Impure World Reincarnation is how much control to exert over the reincarnated soul. After first performing it the user is only able to restrict their movements. In general, this limited control is not an issue for the summoner, and they will typically "deactivate" the reincarnation, placing them in a coffin for storage and transportation until they're needed. However, when the perfected Impure World Reincarnation is used to revive somebody, there comes a possibility that they will be strong enough to resist this control; Orochimaru notes Hashirama Senju could break free if he chose to.6 In order to actually be able to control their actions, the user must implant a special talisman - generally attached to the end of a kunai - within the reincarnation's brain. The talisman's design determines how strong the control is: * At its most basic, the reincarnated soul retains their personality, giving them the freedom to approach a given task however they like so long as it broadly carries out the summoner's bidding. On the one hand, this makes them more useful in combat because they know how best to use their own abilities7 and, if deployed against somebody they knew when they were alive, there is a possibility for psychological warfare.8 On the other hand, although they are compelled to do as their summoner wishes and act without reluctance,9 they can undermine their summoner to a degree, either by making poor decisions that opponents can take advantage of or by giving opponents advice about how to defeat them.10 Despite its risks, Kabuto prefers this level of control. * At its strongest level, the reincarnated soul's personality is entirely eliminated. The summoner instead controls all of their actions, even permitting them to speak through the reincarnation11or summon other reincarnated souls to their location. Although this guarantees the reincarnated soul will only ever act as desired, they are less resourceful and it requires the summoner's attention for every action that must be taken, making it difficult for them to multi-task depending on the circumstances. Orochimaru prefers this level of control. Kabuto has at times rewritten talismans remotely in order switch to this level of control when the situation calls for it.12 Kabuto and Orochimaru are able to strengthen the bindings they use through external means: Kabuto siphons chakra from the cursed seal Anko Mitarashi is branded with;12 Orochimaru usesSenju cells.13 Relatedly, any level of control creates a traceable chakra signature between the reincarnated soul and their summoner, allowing reincarnated sensors to trace the summoner's location.14 Attributes When first summoned, the body will appear grey and in a state of minor decay: marred by cracks and other imperfections. If the summoner chooses to, they can rejuvenate the reincarnation while planting their control talisman, restoring their complexion and reducing some of the imperfections; this is merely aesthetic and the signs of decay do not inhibit their abilities. An unavoidable characteristic of a reincarnated body is the darkened sclerae, with a soul that retains its personality having gray sclerae and a soul with a suppressed personality having black sclerae.4 A reincarnated individual will have all the abilities they had during their life, including kekkei genkaiand kekkei tōta. They are psychically restored as they were at the time of their death, including any physical handicaps they may have possessed, such as Nagato's damaged legs. Exceptions exist: illnesses they had will not be preserved, nor will any physical damage that contributed to their death. There is some inconsistency of whether or not foreign body matter will be restored as well:Hanzō retains the poison gland of the black salamander, but Madara Uchiha does not have access toHashirama Senju's genetic material and thus Kabuto must artificially reproduce it for him. Clothing is reproduced according to what they wore when they died, although it is merely a superficial aspect of their reincarnated body; armor offers no actual protection, being of the same ashen material as the rest of their body. Reincarnated members of Akatsuki are, however, outfitted with different cloaks than they used to wear. Weaponry is usually not retained and must instead be gathered by the summoner; the reincarnated Seven Ninja Swordsmen of the Mist only have access to those swords Kabuto is able to acquire.15 One exception seems to be the Gold and Silver Brothers'Treasured Tools of the Sage of the Six Paths, which are still seemingly stored within the brothers' bodies.16 Despite being largely the same as they were while alive, the reincarnated can never be as powerful, even with the perfected Impure World Reincarnation; Madara's reincarnated body is successfully bound by the Sage Art: Gate of the Great God, which he easily breaks free of as soon as he isrestored to life.17 Likewise, there are some things a reincarnated body simply cannot do, such as access all the abilities of the Rinnegan or become the jinchūriki of the Ten-Tails.18